1. Field of the Invention
This invention relates to a radiation image read-out apparatus for exposing a stimulable phosphor sheet having a radiation image stored thereon to stimulating rays which cause it to emit light in proportion to the stored radiation energy, photoelectrically detecting the emitted light, and obtaining a read-out image signal for use in reproduction of a visible image. This invention particularly relates to a radiation image read-out apparatus provided with a storage means for storing the read-out image signal in an image file, i.e. a radiation image read-out and image signal storing apparatus.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. No. 4,258,264 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet) is first exposed to a radiation passing through an object to have a radiation image stored thereon, and is then scanned with stimulating rays such as a laser beam which cause it to emit light in the pattern of the stored image. The light emitted by the stimulable phosphor sheet upon stimulation thereof is photoelectrically detected and converted to an electric image signal, which is processed as desired to reproduce a visible image on a recording medium such as a photographic light-sensitive material or on a display device such as a cathode ray tube (CRT).
The radiation image recording and reproducing system using a stimulable phosphor sheet is advantageous over conventional radiography using a silver halide photographic material in that the image can be recorded over a very wide range (latitude) of radiation exposure and further in that the electric signal used for reproducing the visible image can be freely processed to improve the image quality for viewing, particularly for diagnostic purposes. In more detail, since the amount of light emitted upon stimulation after the radiation energy is stored on the stimulable phosphor varies over a very wide range in proportion to the amount of energy stored thereon, it is possible to obtain an image having desirable density regardless of the amount of exposure of the stimulable phosphor to the radiation by reading out the emitted light with an appropriate read-out gain and converting it to an electric signal to reproduce a visible image on a recording medium or a display device. The electric signal may further be processed as desired to obtain a radiation image suitable for viewing, particularly for diagnostic purposes. This is very advantageous in practical use.
In the aforesaid radiation image recording and reproducing system, image signals may be directly obtained as digital signals. On the other hand, in recent years, digital storage has attracted attention for the reasons described below. Namely, when image information is stored as digital signals, it may be maintained without deterioration unlike the case where it is stored in the form of X-ray films. Also, it is possible to store much image information in a small storage space by utilizing a high-density recording medium such as an optical disk.
However, since the amount of information on radiation images is enormous, unlike documents or the like, the storage space is not reduced much by the use of optical disk storage techniques. Further, since the cost of the recording medium is high, the storage cost per image is not so low.